This invention relates generally to apparatus for writing and/or reading information on disklike record media such as flexible magnetic disks, and more specifically to such apparatus of the class having a drive pin resiliently supported in an eccentric position on a turntable, the drive pin being engageable in an eccentric opening in the record medium for imparting the rotation of the turntable thereto. Still more specifically, the invention deals with an improved support mechanism for the drive pin of such rotating disk data storage apparatus.
A flexible magnetic disk having an eccentric slot to be engaged by a drive pin, and a disk drive for use therewith, are both described and claimed in U.S. Pat. No. 4,445,157 to Takahashi. The magnetic disk proposed by this patent has a diameter of three and a half inches and is rotatably housed in a generally flat, boxlike envelope of relatively rigid plastic material to make up a disk cassette. The magnetic disk has a rigid hub of magnetic material attached centrally thereto. The hub has defined therein a central opening of square shape and an eccentric opening of rectangular shape.
When positioned in the associated disk drive, the magnetic disk has its central hub placed on a turntable which is much less in diameter than the disk. The turntable has a permanent magnet mounted thereon for attracting the disk hub. Disposed centrally on the turntable, a spindle engages in the central opening in the disk hub for centering the disk on turntable. A drive pin is disposed eccentrically on the turntable for driving engagement in the eccentric opening or slot in the disk hub, imparting the rotation of the turntable to the magnetic disk.
The drive pin must be resiliently supported on the turntable for displacement both radially inwardly of the turntable and parallel to the axis of the spindle. The radially inward displacement of the drive pin is necessary for holding the disk in proper positional relationship with the turntable as the drive pin imparts the rotation of the turntable to the disk. The drive pin displacement parallel to the spindle axis is intended to cause the drive pin to spring into driving engagement in the eccentric slot in the disk hub after the turntable starts rotation in sliding contact therewith.
The three and a half inch magnetic disk has no index hole formed therein. The required index pulses are generated by photoelectrically or magnetoelectrically sensing an index mark formed on a part, such as a part of a disk drive motor, that rotates with the disk. The maintenance of proper positional relationship between the drive pin and the disk is therefore of utmost importance.
Conventionally, for resiliently supporting the drive pin as above, a planar leaf spring was employed, as described and claimed in U.S. Pat. No. 4,758,915 filed by Sakaguchi and assigned to the assignee of the instant application. The planar drive pin support spring was cantilevered, bored at one end to fit over the spindle and carrying the drive pin on the other end. Disposed parallel to the turntable, the planar drive pin support spring permitted easy displacement of the drive pin parallel to the spindle axis. For drive pin displacement radially inwardly of the turntable, on the other hand, the planar drive pin support spring underwent torsional displacement, thereby causing the drive pin to slant in the required direction.
This prior art device proved unsatisfactory as the drive pin slanted radially inwardly of the turntable upon establishment of driving engagement in the eccentric slot in the disk hub. There would be no problem at all if the drive pin slanted through the same angle, because then the magnetic disk would be in the same angular position relative to the drive pin. In practice, however, it is difficult to cause the drive pin to slant through the same angle. The result was variations in the angular position of the disk relative to the turntable and, in consequence, to the index mark on the disk drive motor. Such misplacement of the disk on the turntable could be a bar to correct data transfer between the disk and associated transducers.
In order to overcome the noted weakness arising from the slanting attitude of the drive pin upon driving engagement in the eccentric slot in the disk hub, it has been suggested to mount the drive pin support spring on the turntable for pivotal movement in a plane parallel to that of the turntable. The drive pin was mounted on one end of the support spring, and another spring was connected between the other end of the support spring and the turntable for biasing the drive pin approximately radially outwardly of the turntable. No substantial slanting of the drive pin became necessary according to this second prior art device.
However, the slanting of the drive pin was not totally eliminated, so that the angular position of the disk was still variable relative to the turntable. It must also be taken into consideration that the distance between the central opening and the eccentric slot in the hub of the magnetic disk is not necessarily the same but subject to change from one disk to another. The pivotal displacement of the drive pin about the fixed axis of the support spring was ineffective to thoroughly avoid variations in the angular position of the disk relative to the turntable in such cases.